Surgical chisel

ABSTRACT

A chisel includes a hammered portion to be hammered which is provided so as to project from a middle or an end of a handle and extend to pass through a portion on an extended line in the direction opposite to the direction of the blade. Even if the chisel is hammered in a state where a tip of the blade thereof is not inserted into a bone, the chisel easily advances in the direction of the blade, thereby reducing a possibility that the blade slides on a surface of the bone.

This application claims the benefit of priority to International PatentApplication No. PCT/JP2009/068082 filed Oct. 13, 2009 claiming priorityupon Japanese Patent Application No. 2008-309109 filed Nov. 6, 2008, ofwhich full contents are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an angled chisel used for cutting abone of a lumbar spine in minimally invasive surgery for lumbar spinalcanal stenosis.

2. Description of the Related Art

FIG. 1 is an axial cross-sectional view illustrating a normal lumbarspinal canal. A lumbar spinal canal 1 is a lumen surrounded by a facetjoint 2, a ligamentum flavum 3, a vertebral arch 4, an intervertebraldisc, and the like. A spinal cord, a dura mater, and nerve roots run inthe lumbar spinal canal 1. The lumbar spinal canal stenosis is a diseasewhich causes neurological symptoms in legs by narrowing of the spinalcanal due to hypertrophy of the facet joint, hyperplasy of theligamentum flavum, or the like as illustrated in FIG. 2.

Posterior decompression which is common as a surgery treatment for thelumbar spinal canal stenosis is a therapeutic approach in which bones ofthe vertebral arch and the facet joint are partially excised and theligamentum flavum is also excised so as to expand the spinal canal. Assuch posterior decompression, an operative procedure which is recentlyspread as the minimally invasive surgery is a micro endoscopicdiscectomy (MED). The MED is an operative procedure in which a tubularretractor having a diameter of slightly smaller than 2 cm is installedat the backside of the vertebral arch and the surgery is completed inthe tubular retractor under an endoscope. A spinous process and asupraspinous ligament are important as lumbar spine posteriorstabilizing mechanisms. With the MED, these tissues can be conserved andinvasion of muscles around these tissues can be minimized.

In the MED, an operation is performed in an inner side of a tubularretractor 5 which is an elongated tube as illustrated in FIG. 2.Therefore, a surgical region is limited by an angle and a position ofthe tubular retractor. An upper portion of the tubular retractor cannotbe inclined to the side of a spinous process 6 due to obstruction of thespinous process 6 at the approach side. Therefore, there has been aproblem that an angle at which a medial facet is cut at the approachside is as indicated by a solid line 7 and decompression at the approachside cannot be sufficiently made unless extensive bone is excised.Further, if too much bone is excised, many portions of the facet jointare removed or facet fracture is caused. This causes a risk thatinstability is increased.

In order to conserve the facet bone as indicated by bone-cutting linesof dashed lines 8 as much as possible, it is ideal that a bone is cutoutward so as to excise the medial facet at the approach side moreselectively. In order to achieve such an object, a chisel of which bladeis bent with respect to a handle is already present. However, as a userhammers the chisel so as to advance the chisel, the chisel does notadvance in the direction of the bending blade and slides in many cases.

This is because a point 10 to be hammered is located not on an extendedline 12 in the direction opposite to the direction of the blade 11 buton an end of a handle 9 for gripping on the chisel as illustrated inFIG. 3. If the chisel is hammered in a state where a tip of the bladethereof is not inserted into a bone, the chisel advances on a line 13connecting the tip of the chisel and the point 10. That is, in such acase, the chisel does not advance in the direction of the blade andslides on a surface of the bone.

SUMMARY OF THE INVENTION

In order to solve the above problem, an object of the invention is toprovide a chisel for cutting a bone easily in the direction of a bladeon an angled chisel used when a bone of a lumbar spine is cut inminimally invasive surgery for lumbar spinal canal stenosis.

A surgical chisel includes a blade, a handle having a gripping portion,and a hammered portion to be hammered as a main structure. The blade isbent with respect to the handle. Further, the hammered portion isarranged so as to project from the handle and extend to pass through aportion on an extended line opposite to the direction of the blade.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a normal lumbar spinalcanal.

FIG. 2 is a cross-sectional view illustrating a spinal canal of lumbarspinal canal stenosis.

FIG. 3 is a side view illustrating a conventional angled chisel.

FIG. 4 is a side view according to a reference example.

FIG. 5 is a side view according to a preferred embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

A reference example is described with reference to FIG. 4. Asillustrated in FIG. 4, a chisel includes a blade 14, a handle 15 forgripping, and a hammered portion 16 to be hammered as a main structure.The blade 14 is bent with respect to the handle 15. The handle 15 isconstituted by a grip 17 and a shaft 18. The grip 17 is a portion whichis made thick for being gripped by hand. The shaft 18 is continuous tothe blade 14. The hammered portion 16 is a hard structure which iscontinuous to an end of the handle 15 in a bending manner. Further, thehammered portion 16 has an arc shape as drawn about a tip of the blade14 as a center point and has such length that the hammered portion 16passes through a portion on an extended line in the direction oppositeto direction of the blade.

If a portion of the hammered portion 16, which corresponds to a portionon the extended line in the direction opposite to the direction of theblade, is hammered, the chisel tends to advance in the direction of theblade. The direction in which the blade advances can be finely adjustedas follows. That is, the hammered portion 16 is hammered at the furthertip side when a surface of a bone is hard so that the blade easilyslides. Or the hammered portion 16 is hammered at the further handleside when a user desires to advance the chisel in the axial direction ofthe handle.

A preferred embodiment of the invention is described with reference toFIG. 5. A chisel includes a blade 19, a handle 20 for gripping, and ahammered portion 21 to be hammered as a main structure. The blade 19 isbent with respect to the handle 20. The handle 20 is constituted by agrip 22 and a shaft 23. The grip 22 is a portion which is made thick forbeing gripped by hand. The shaft 23 is continuous to the blade 19. Thehammered portion 21 is a hard structure which is branched from a lowerend of the grip 22 of the handle 20 so as to extend in the directionopposite to the bending direction of the blade 19. Further, a hammeredpoint 24 is attached to the hammered portion 21 near a portion on anextended line in the direction opposite to direction of the blade.

EFFECT OF THE INVENTION

A point to be hammered is located near a portion on a straight line ofthe direction of the blade. Therefore, even if the chisel is hammered ina state where a tip of the blade thereof is not inserted into the bone,the chisel easily advances in the direction of the blade, therebyreducing a possibility that the blade slides on a surface of the bone.

Therefore, a bone can be cut outward so as to excise the medial facet atthe approach side more selectively. Therefore, bones and joints can beconserved as much as possible.

What is claimed is:
 1. A surgical chisel comprising: a handle includinga shaft and a grip, the shaft and the grip being co-axial; a blade whichis provided at a tip of the shaft and bent with respect to the handle;and a hammered portion which is branched from a lower end of the grip,wherein, in side view, the hammered portion and the blade extend inopposite lateral directions with respect to the axis of the shaft andthe grip, and wherein the grip is thicker than the shaft.
 2. Thesurgical chisel according to claim 1, wherein, in side view, a hammeredpoint at an end of the hammered portion extends toward a linecorresponding to the longitudinal axis of the blade.
 3. The surgicalchisel according to claim 1, wherein an entirety of the grip is thickerthan the shaft, and wherein the hammered portion is branched from apoint proximal to a transition point between the grip and the shaft. 4.The surgical chisel according to claim 1, wherein the hammered portionis integral with the grip.